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EPA 2015 Tier IV emission requirements pose significant challenges to large diesel engine aftertreatment system (EAS) development aimed at reducing exhaust emissions such as NOx and PM. An EAS has three primary subsystems, Aftertreatment hardware, controls and fluid delivery. Fluid delivery is the subsystem which supplies urea into exhaust stream to allow SCR catalytic reaction and/or periodic DOC diesel dosing to elevate exhaust temperatures for diesel particulate filter (DPF) soot regeneration. The purpose of this paper is to discuss various aspects of fluid delivery system development from flow and pressure perspective. It starts by giving an overview of the system requirements and outlining theoretical background; then discusses overall design considerations, injector and pump selection criteria, and three main injector layouts. Steady state system performance was studied for manifold layout.

Selective Catalytic Reduction (SCR) has become a mainstream approach to reduce diesel engine NOx emissions. Urea Water Solution (UWS) injection and interactions with mixers and exhaust gases affect the homogeneity of ammonia distribution at catalyst inlet and solid deposits formation on walls / mixer surfaces, therefore influencing SCR performance and durability. Computational Fluid Dynamics (CFD) is used to simulate an EU V compliant SCR system with a dual baffle mixer for heavy duty diesel engines. The modeling procedure is carried out by a multi-dimensional CFD code CONVERGE that includes transient urea transport processes in an exhaust flow configuration, detailed spray break-up, evaporation, wall-film, turbulence, and Conjugate Heat Transfer (CHT) models as well as an automated mesh generation approach. Locations of urea deposits and system pressure drop are predicted and validated against measurements, providing uniformity index (UI) predictions at the catalyst inlet.

To meet EPA Tier IV large diesel engine emission targets, intensive development efforts are necessary to achieve NOx reduction and Particulate Matter (PM) reduction targets [1]. With respect to NOx reduction, liquid urea is typically used as the reagent to react with NOx via SCR catalyst [2]. Regarding to PM reduction, additional heat is required to raise exhaust temperature to reach DPF active / passive regeneration performance window [3]. Typically the heat can be generated by external diesel burners which allow diesel liquid droplets to react directly with oxygen in the exhaust gas [4]. Alternatively the heat can be generated by catalytic burners which enable diesel vapor to react with oxygen via DOC catalyst mostly through surface reactions [5].

EPA 2015 Tier IV emission requirements pose significant challenges to large diesel engine after treatment system development with respect to reducing exhaust emissions including HC, CO, NOx and Particulate Matter (PM). For a typical locomotive, marine or stationary generator engine with 8 to 20 cylinders and 2500 to 4500 BHP, the PM reduction target could be over 90% and NOx reduction target over 75% for a wide range of running conditions. Generally, HC, CO and PM reductions can be achieved by combining DOC, cDPF and active regeneration systems. NOx reduction can be achieved by injecting urea as an active reagent into the exhaust stream to allow NOx to react with ammonia per SCR catalysts, as the mainstream approach for on-highway truck applications.

The introduction of stringent EPA 2015 regulations for locomotive / marine engines and IMO 2016 Tier III marine engines initiates the need to develop large diesel engine aftertreatment systems to drastically reduce emissions such as SOx, PM, NOx, unburned HC and CO. In essence, the aftertreatment systems must satisfy a comprehensive set of performance criteria with respect to back pressure, emission reduction efficiency, mixing, urea deposits, packaging, durability, cost and others. Given multiple development objectives, a systematic approach must be adopted with top-down structure that addresses top-level technical directions, mid-level subsystem layouts, and bottom-level component designs and implementations. This paper sets the objective to provide an overview of system development philosophy, and at the same time touch specific development scenarios as illustrations.

With introductions of stringent diesel engine emission regulations, the DOC and DPF systems have become the mainstream technology to eliminate soot particles through diesel combustion under various operation conditions. Urea-based SCR has been the mainstream technical direction to reduce NOx emissions. For both technologies, low-temperature conditions or cold start conditions pose challenges to activate DOC or SCR emission-reduction performance. To address this issue, mini or full flow burner systems may be used to increase exhaust temperature to reach DOC light-off or SCR initiation temperature by combustion of diesel fuel. In essence, the burner systems incorporate a fuel injector, spray atomization, proper fuel / air mixing mechanisms, and combustion control as independent heat sources.

Hybrid bulldozers use less fuel by providing better efficiency and fewer emissions, which was confirmed by one Caterpillar application of D7E in the market in 2010. To take advantages of the series hybrid bulldozer system, Chinese government launched similar hybrid bulldozer with independent double motor design. The Hybrid Bulldozer Power-Train system includes 14 components including motor, motor control system, engine, super capacitor to BMS and etc. This specific hybrid architecture, compared with D7E, removes the complicated hydraulic steering system. Instead, the steering function was developed by running both traction motors, further simplifying the power-train system. A Diesel engine is used to propel the attached generator to produce AC power which is then converted to DC power and connected with the main power link (super capacitor). DC power is finally converted back to AC to propel those two independent traction motors. CAN network is applied for communication.

The introduction of stringent EPA 2015 regulations for locomotive / marine engines and IMO 2016 Tier III marine engines initiates the need to develop large diesel engine aftertreatment systems to drastically reduce emissions such as SOx, PM, NOx, unburned HC and CO. In essence, the aftertreatment systems must satisfy a comprehensive set of performance criteria with respect to back pressure, emission reduction efficiency, mixing, urea deposits, packaging, durability, cost and others. For on-road and off-road vehicles, urea-based SCR has been the mainstream technology to reduce NOx emissions. For category II marine engines with single cylinder displacement volumes between 7 liters and 30 liters, IMO III (Tier IV) emission regulations dictate approximately 80% reduction of NOx emissions vs. Tier II emission regulations [1]. Urea / ammonia SCR is being considered as an enabling technology to achieve IMO III regulations without significant impacts on engine performance and fuel economy.